How do i deactivate the alarm on atomic projection alarm?

You did not mention model. However, see the page 10 of this manual to disable alarm. It may help.
PCR325W1 Atomic Projection Clock User Manual PCR325W-IM(Hammacher Schlemmer)0882-13 Eng.ai Hideki Electronics (fccid.io)

HITO 6 Alarm Clock Date and Temperature Display

if its atomic it needs to be in a place were it can receive the signal well, put it on auto & leave it on a window sill for a while & it will set its self, mine does.

http://www.lacrossetechnology.com/5110/manual.pdf

Please check out this answer:
http://www.fixya.com/support/t3486802-set_clock

press the alarm button (so the alarm time is on the screen) then the + button. do the same to deactivate the alarm.
it took me forever to work this out after losing my instructions, feel a bit of an idiot now it seems so simple

I had the exact same problem, and found the answer on the Chaney Instrument FAQ page. There's no real solution, but here is the explanation:
Q: My wireless weather station periodically beeps, why?
A: Make sure that any alert and/or alarm features are deactivated first. Constant, sporadic beeping is generally due to the unit’s ability to detect a foreign radio frequency of another wireless unit when that unit transmits a signal. Wireless devices that may cause beeping but are not limited to these devices are; scanners; computers w/wireless keyboard/mouse; or other wireless weather instruments. Essentially, any wireless devices transmitting on a radio frequency have the potential to interfere with each other. Limit the amount of wireless devices to lesson the chance of interference. When beeping occurs, one device will need to be deactivated.

See here for how to set the time, and here for how to set the alarm.

No. I didn't "fiix" it. I only wanted to know how to set it. I have lost the instructions. Thanks, Pat

try looking up the manual on the model number you might find it online. I have the maual for this model.